DESCRIPTION (Verbatium from the Abstract): Hearing impairment is commonly experienced as loss of sensitivity to weak sounds, while intense sounds can remain as loud as in normal hearing. Many current hearing aids treat this phenomenon of loudness recruitment" with sound amplification that decreases with sound intensity, to provide normal loudness. Design of such compressive amplifiers is controversial. In research sponsored by the NIH the PI developed models of nonlinear cochlear sound processing, which suggest compression strategies that prevent overamplification while minimizing distortion and disturbance by background noise. In Phase-I, algorithms were developed for multichannel hearing aids using both rapid and slow compression mechanisms. Benefits of the new design were demonstrated with a computer simulation in pilot tests on normal and impaired hearing subjects for their understanding of speech in iroise. New insights are provided on functions of nonlinear cochlear mechanisms lacking in impaired ears. An advanced real-time implementation was developed in Phase-I. In Phase-II, prototype wearable hearing aids will be developed, fabricated, and formally tested by independent laboratories. Preliminary simulations of custom miniaturization technologies will be conducted in preparation for commercialization. In addition, the design will be developed as a desktop master hearing aid for clinical optimization of individual fittings. PROPOSED COMMERCIAL APPLICATION: Wider acceptibility of hearing aids is potentiated by the superior performance of the new design, particularly in background noise. The fundamental relationship of the new design to cochlear mechanisms potentiates a professional-instrument market for a full-featured master hearing aid for use in R & D and clinical fitting.